This is a randomized trial of two different methods of administering 5- FU plus leukovorin in the treatment of colon cancer. Samples of the tumor will be assayed for thymidylate synthase (TS) message by RT-PCR, following which the patients will be randomized to receive intermittent high dose 5-FU infusion or continuous low dose infusion. Patients will continue to receive the same therapy until either toxicity or poor response occurs. Response will be correlated with apparent TS levels.